1. Field of the Invention
The present invention relates to large-current superconducting wire material for use in nuclear fusion reactors, energy storage apparatuses and other such devices.
2. Description of the Prior Art
In the prior art there is used forced cooled type multi-filament superconducting wire formed of stabilizer and several hundred superconductor filaments twisted together, with each filament being about one millimeter in diameter, arranged inside stainless steel conduit pipe.
When the superconductor is Nb.sub.3 Sn or an alloy of Nb.sub.3 Sn, a problem is that the critical current density of the superconductor is degraded to some 20 to 40 percent below that of the multi-filament superconducting wire of Nb.sub.3 Sn or Nb.sub.3 Sn alloy. It is considered that this may be the result of compressive strain on the Nb.sub.3 Sn arising from the difference between the thermal shrinkage factors of the Nb.sub.3 Sn and the stainless steel.
One possible solution is to use, as the conduit material, a nickel alloy such as Incoloy 908 that has substantially the same thermal shrinkage factor as Nb.sub.3 Sn, and a high tensile strength at the temperature of liquid helium (hereinafter referred to as "4K"). However, because such alloys are ferromagnetic and also have problems with respect to corrosion-resistance, they have not yet been applied as a conduit material.
Titanium (pure titanium and titanium alloy) is a non-magnetic, highly corrosion-resistant material with a thermal shrinkage factor which is close to that of Nb.sub.3 Sn, and its excellent balance of strength and toughness at very low temperatures makes it an excellent prospect as a material for conductor conduit in superconducting coil.